This invention relates to a control serum useful in a field of clinical diagnosis using a dry analytical element.
Diagnosis of human illness by analyzing a specimen such as blood or urine has been prosecuted for a long period of time. To analyze an analyte(s) in the specimen, there are two processes. That is to say, a wet process in which an aqueous solution is prepared by adding reagents necessary for a designed analysis and a specimen in water to produce some reaction between them, and a dry process in which a specimen is supplied to a layer (for example, a layer of gelatin) containing reagents in advance in a dry state to produce some reaction between them in the layer.
When either of the above-mentioned methods is carried out, a control serum is employed to draw up a calibration curve or to quality control of analysis. Generally, the control serum is prepared using human serum or bovine serum from which fibrin is eliminated as raw material and then removing calcium ions from it used for elimination of fibrin through a dialysis processing. In the dialysis processing, some components with low molecular weight are also lost at the same time. Then, a necessary component (e.g. pure substance, an enzyme or the like) is added to adjust concentration of the serum. Further, a surfactant, an antiseptic agent (an antibiotic or the like) or an activating agent (NAC for CK or the like) is sometimes added.
Conventionally, a control serum based on the serum that has been once dialyzed is used in either of two processes above mentioned. The control serum is manufactured by following steps in outline. Only plasma is collected as a component of blood using a blood collecting tube containing an anticoagulant in it. Then plural plasma samples thus collected are mixed to prepare pooled plasma. The pooled plasma is added with Ca2+ ions and subjected to processing of elimination of fibrin to obtain pooled serum rich in Ca2+ ions. Then, the pooled serum rich in Ca2+ ions is dialyzed to remove excess Ca2+ ions to prepare the pooled serum for raw material of the control serum.
However, when the control serum prepared by the above-mentioned process is used, such problem has occurred that results of measurement of the same specimen obtained by the wet process and the dry process show misfit each other. An actual example for UA is shown in FIG. 1. In FIG. 1, ▴ illustrates the result obtained using the control sample of the Japan Medical Association, and ◯ illustrates the result obtained using human raw serum, respectively. In the case where the accuracy control sample of the Japan Medical Association is used, the result of the dry process shows higher value than that of the wet process. Though not shown in the figure, results concerning BUN and CRE were similar.
One method to solve the problem is disclosed in JP 2000-131323 A. According to the method, reactivity of a control serum similar to that of a fresh human serum is assured by adding buffering agents such as bicarbonates, 6-aminocaprone or the like to commercially available control serums. However, some problems still remain when utilizing the method, such that prescription may be changed when a commercially available control serum is displaced by another one, an additional processing is required and it is difficult to say that availability for the all test necessary for clinical analysis has been confirmed or the like.